The present invention relates to a color picture tube having an improved inline electron gun with coma correction members, and particularly to an improvement in the gun that facilitates its fabrication.
An inline electron gun is one designed to generate or initiate preferably three electron beams in a common plane and direct those beams along convergent paths to a point or small area of convergence at the tube screen.
A problem that exists in a color picture tube having an inline gun is coma distortion, wherein the sizes of the electron beam rasters scanned on the screen by an external magnetic deflection yoke are different because of the eccentricity of the two outer beams with respect to the center of the yoke.
There are many patents that disclose various coma correction members located at the exits of the electron guns. These members affect fringe portions of the magnetic deflection fields to either enhance or shunt the fields at the electron beam paths. One such patent is U.S. Pat. No. 4,556,819, issued on Dec. 3, 1985 to Chen et al., wherein four coma correction members are attached to the inside bottom of a shield cup. The positioning of the members relative to each other and relative to the electron beams is very important for achieving proper coma correction. However, it is sometimes difficult to accurately position the members on the bottom of the shield cup because of interference from the shield cup sidewalls.